The development history of mobile communication shows that cell splitting, a greater bandwidth and higher spectrum efficiency are three may support of system capacity improvement. Therefore, “cell splitting” may be a key of achieving a capacity increase objective of a 5th-Generation (5G) system.
A 4th-Generation (4G) system may obtain a cell splitting gain through a Heterogeneous Network (HetNet). In the HetNet, low-power Transmission Points (TPs) may be flexibly and sparsely deployed in a coverage area of a macro cell Evolved Node B (eNodeB or eNB) to form a multilayer network composed of macro cells and small cells. The HetNet may not only ensure coverage, simultaneously improve cell splitting flexibility and system capacity and share service pressure of the macro cell, but also extend coverage of the macro cell. At the end of researches on 4G systems, for further improving system capacity, the Third Generation Partnership Project (3GPP) puts forward a small cell enhancement technology, and carries out preliminary researches on problems appearing during high-density deployment of small cells.
An Ultra Dense Network (UDN) is put forward under such a background, and it may be considered as a further evolution of the small cell enhancement technology. In the UDN, a density of TPs will be further increased, coverage of each TP may be further narrowed (dozens of meters and even a dozen meters), and each TP may serve only one or few users at the same time. Ultra-dense deployment shortens distances between the TPs and terminals (or called as User Equipment (UE)), which may effectively reduce their transmitted power. Since the TPs and terminals get very close, differences between uplinks and downlinks are smaller and smaller.
A Backhaul Link (BL) is a key problem to be solved by a UDN, and may directly relate to deployment cost, capacity and performance of various solutions of the UDN. Nodes in the UDN may be divided into two major categories, i.e. nodes using self-Backhaul Links (sBLs) and nodes using non-self-backhaul links (nsBLs). Self-backhaul means that the same wireless transmission technology and frequency band are used for a BL and an Access Link (AL), where the BL and the AL may implement multiplexing in a time division or frequency division manner. A node using an nsBL uses a transmission technology (for example, a Wireless Fidelity (WIFI) technology and an Asymmetric Digital Subscriber Line (ADSL) technology) and medium (for example, an optical fiber and a cable) different from the AL.
For many application scenarios (for example, a dense block) of a UDN, cost in deployment of a wired backhaul (for example, deployment or leasing cost of a cable or an optical fiber, and selection and maintenance cost of a station location) is usually unacceptable, and unplanned deployment cannot be implemented. In addition, if a wired BL is provided according to a maximum system capacity, a utilization rate of the BL may be very low, and investment cost is greatly wasted. The reasons for such deficiency are listed below.
Under a condition that TPs are densely deployed, each TP may serve a relatively smaller number of users, and thus has a great load fluctuation.
Considering the aspects of energy saving, interference control or the like, some TPs may be dynamically enabled or disabled, so that BLs may be in an idle state most often.
A content prediction and caching technology may widen a fluctuation range of a BL resource requirement.
A microwave may be frequently used as a BL of a macro eNB, but its application in a UDN may be greatly limited. On one hand, the microwave may increase hardware cost of a low-power TP. Different from the macro eNB, cost of the low-power TP in the UDN is relatively low, and microwave hardware may occupy relatively more of the hardware cost of the whole cost. Second, the microwave may also increase additional spectrum cost. If an unlicensed spectrum is adopted, it may usually be very difficult to control interference, and transmission quality of a BL cannot be guaranteed. More importantly, an antenna height of a TP in a main scenario of the UDN is relatively smaller, and the microwave may be more likely to be blocked to cause a strong fluctuation of quality of the BL.
From the above analysis, it can be seen that a self-backhaul technology is very attractive in a UDN. It does not require any wired connection, may support unplanned or semi-planned deployment of TPs, and effectively reduces deployment cost. Sharing a spectrum and a wireless transmission technology with an AL may reduce spectrum and hardware cost. By joint resource allocation of an AL and a BL, a system may adaptively regulate a resource allocation proportion according to a network load condition to increase resource utilization efficiency. In addition, due to use of a licensed spectrum, joint optimization of the wireless sBL and the AL can effectively guarantee quality of a wireless sBL and greatly improve transmission reliability.
After a wireless sBL is used, a network may be divided into three layers (as shown in FIG. 1).
(1) Macro eNBs or micro eNBs form a macro cell (a first layer network), which may obtain data from a core network and may be configured to provide coverage.
(2) Donor TPs (dTPs) (which may be pico or Remote Radio Head (RRH)) may form a second-layer network, which may obtain data from the core network or the first-layer network by virtue of an nsBL (for example, an optical fiber) and may be configured to acquire a cell splitting gain.
(3) Relay TPs (rTPs) may form a third-layer network, which may obtain data from the second-layer network through an sBL, and may be configured to improve coverage of a UDN, implement unplanned deployment of TPs and further increase capacity of the UDN.
The inventor of the application finds in a research process of the above technology that an sBL may consume a resource of an AL and may influence overall capacity of a network. Therefore, how to enhance performance of an sBL and increase a utilization rate of a radio resource becomes an important research direction. Flexible sBL/AL resource allocation may serve important means for increasing capacity of an sBL. The flexible sBL/AL may flexibly regulate a resource proportion between different links according to channel states of the sBL and an AL to achieve a purpose of fully utilizing radio resources. In addition, a content prediction and caching technology widely researched in the industry at present makes flexible resource allocation between the sBL/AL more important. This technology predicts a content to be accessed by a user in the future and caches related data in an rTP in advance, thereby greatly reducing a load of the sBL. For example, for a certain UE served by an rTP, when a downlink data packet is delivered from a core network, it may be necessary to simultaneously allocate resources to an sBL and an AL. When the data packet has been cached in the rTP, no sBL resource is required to be allocated to the rTP, and the corresponding sBL resource needs to be rapidly allocated to the AL.
A Long Term Evolution (LTE) Release 10 (R10) relay is communication equipment, applied most widely at present, using a wireless sBL. LTE R10 relays may be divided into Frequency Division Duplexing (FDD) R10 relays and Time Division Duplexing (TDD) R10 relays, corresponding to two LTE frame structures respectively. A regulation period of an sBL/AL resource proportion supported by an LTE R10 relay is very long (far longer than 1 second), and cannot meet a flexible sBL/AL resource allocation requirement. In addition, an LTE R10 relay does not support flexible resource allocation between an uplink and downlink of an AL or an sBL.
An AL and sBL of an LTE R10 relay may adopt Time Division Multiplexing (TDM) to implement multiplexing. A dTP may transmit a downlink signal of an sBL at data parts of some Multimedia Broadcast multicast service Single Frequency Network (MBSFN) subframes of a downlink subframe (i.e. an FDD subframe or TDD downlink subframe) of an AL of an rTP, and may also allocate some subframes for transmitting an uplink signal of the sBL on an uplink subframe (i.e. a subframe on an FDD uplink carrier frequency or a TDD uplink subframe) of the AL of the rTP. A control domain (located at first one or two Orthogonal Frequency Division Multiplexing (OFDM) symbols) of each MBSFN subframe may still be configured to transmit a common pilot and a control channel on the AL of the rTP, as a result, the LTE R10 relay may need to additionally design the control channel (i.e. a Relay Physical Downlink Control Channel (R-PDCCH)) for scheduling a radio resource of the sBL, which may increase implementation complexity of equipment.
FIG. 2 is a resource configuration of a TDD R10 relay. In FIG. 2, an AL uses an uplink and downlink configuration 1, that is, subframes 0, 4, 5 and 9 are downlink subframes, subframes 1 and 6 are special subframes and subframes 2, 3, 7 and 8 are uplink subframes. In the downlink subframes, the subframes 4 and 9 are MBSFN subframes, their control domains transmit reference signals and control channels of ALs, and their data domains are configured to transmit downlink signals of sBLs. The subframe 3 is configured to transmit uplink signals of the sBLs. The control domains of the MBSFN subframes transmit Cell-specific Reference Signals (CRSs)/Physical Control Format Indicator Channels (PCFICHs) (configured to notify OFDM symbol numbers of the control domains)/Physical Downlink Control channels (configured to transmit scheduling signaling related to uplink data transmission)/Physical Hybrid Automatic Repeat Request (ARQ) Indicator Channels (PHICHs) (configured to transmit Acknowledgement (ACK)/Negative Acknowledgement (NACK) signals of uplink data.
Researches made by the inventor of the application show that, in an uplink Hybrid ARQ (HARQ) timing relationship corresponding to a TDD uplink and downlink configuration, an MBSFN subframe corresponding to an sBL uplink subframe or an MBSFN subframe not corresponding to any uplink subframe does not need to schedule an AL for uplink data transmission, a PDCCH/PHICH has no use, and a control domain is only configured to transmit a CRS/PCFICH. Therefore, resources on such MBSFN subframe may be wasted.
In addition, AL/sBL resource configuration types of an LTE R10 relay are limited at present, and cannot meet a flexible AL/sBL resource allocation requirement of a UDN. For example, an LTE R10 relay does not support dynamic allocation of all resources to an AL. However, according to the above analysis, it may be quite necessary for an rTP using a content prediction and caching technology.